As such a horizontal swing clamping apparatus, conventionally, there is an apparatus described in patent literature 1 (Japanese Examined Utility Model Publication No. 18267/1985 (Jitsukoushou 60-18267)). This conventional art is structured as follows.
An annular free piston is inserted between a cylinder hole of a cylinder tube and a piston rod. An inner end portion of a free piston rotation prevention pin is fitted into a straight advance guiding groove provided in a peripheral wall of the free piston, and an outer end portion of the rotation prevention pin is fixed to the cylinder tube. Further, a rotation guiding groove is formed in the peripheral wall of the free piston so as to be opposed to the straight advance guiding groove across the piston rod. An outer end portion of a rotation pin is fitted into the rotation guiding groove, and an inner end portion of the rotation pin is fixed to the piston rod. Furthermore, a piston descent restriction pin is fixed to a lower end of the piston rod. The piston descent restriction pin is configured so as to be able to face a clamping stroke guiding groove of a head cover fixed to a lower portion of the cylinder tube.
In the above-described conventional art, the piston rod (and a clamper) is (are) switched from a released raised position to a locked lowered position according to the following procedure.
First, in a state where both ends of the piston descent restriction pin fixed to a lower portion of the piston rod are received by an upper portion of the head cover, the free piston descends straight down along the straight advance guiding groove. With this, the rotation guiding groove provided in the free piston causes, via the rotation pin, the piston rod (and the clamper) to horizontally rotate in the released raised position. Then, when the both ends of the piston descent restriction pin face the clamping stroke guiding groove and thereby their phases match each other, the piston rod (and the clamper) is (are) driven straight down to the locked lowered position along the clamping stroke guiding groove.